From patchwork Tue Jul 13 11:13:37 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Christian Brauner X-Patchwork-Id: 12373727 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-19.7 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 76DD2C11F66 for ; Tue, 13 Jul 2021 11:16:51 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 627F561288 for ; Tue, 13 Jul 2021 11:16:51 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236014AbhGMLTk (ORCPT ); Tue, 13 Jul 2021 07:19:40 -0400 Received: from mail.kernel.org ([198.145.29.99]:47474 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236007AbhGMLTj (ORCPT ); Tue, 13 Jul 2021 07:19:39 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id EAEB66023F; Tue, 13 Jul 2021 11:16:46 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1626175010; bh=qocQmsJnkDSbWi5OjQ8/N1PrnDUwbWKZRALqNmUZZWw=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=L2I21ATgDi3rUUhAe/zoT1TPWdEopRiUAcz1Ff1LqgscW9Zt2hkWXNfiykploEj1M Kawb1K9bF1o/GAc9m2hBa6eLTpKDs8zzKXvuETUPjDZLj5PYm9KCrCJJuj3jbXCksW 1P2/f5gxh1dcnOatLRmqQ8JeBpbQbuY8RActmD1XsqARI+p85rkpb5laecyJu3aNvY TXikUNwS7z83sFepDiVtrSId2XYwX7PNjhOhom/2NBMHeQsnzYxMuQjCkl+YpKbGW5 u/uYJpf9nt285rSX6fHdn+mpDBFJsVY8I3R09CL5Tkm76s3OjOLU/XD9Ea7FMh5qxR sy/J9ALFfquOA== From: Christian Brauner To: Christoph Hellwig , Chris Mason , Josef Bacik , David Sterba , Al Viro Cc: linux-btrfs@vger.kernel.org, linux-fsdevel@vger.kernel.org, Christian Brauner , Christoph Hellwig Subject: [PATCH 17/24] btrfs/ioctl: allow idmapped BTRFS_IOC_SNAP_DESTROY{_V2} ioctl Date: Tue, 13 Jul 2021 13:13:37 +0200 Message-Id: <20210713111344.1149376-18-brauner@kernel.org> X-Mailer: git-send-email 2.30.2 In-Reply-To: <20210713111344.1149376-1-brauner@kernel.org> References: <20210713111344.1149376-1-brauner@kernel.org> MIME-Version: 1.0 X-Developer-Signature: v=1; a=openpgp-sha256; l=6632; h=from:subject; bh=GQyKvv+ajpx5xbmsj8Uq2YG8bptMKevFTEsMTM2rqcg=; b=owGbwMvMwCU28Zj0gdSKO4sYT6slMSS8LY3533VtV9E18ezri8q8lzRczBX7eGFmnPvHny+P3302 5bN+akcpC4MYF4OsmCKLQ7tJuNxynorNRpkaMHNYmUCGMHBxCsBEVn9g+F9kcFXhAU+9faA7x/lpe2 VnX327vLDR7V2XY1h7zUmG4A0Mf/hEapb6JS35PHNCQpaf15oZjjOnvj/Sy7tBbNX0rDMuPkwA X-Developer-Key: i=christian.brauner@ubuntu.com; a=openpgp; fpr=4880B8C9BD0E5106FC070F4F7B3C391EFEA93624 Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org From: Christian Brauner Destroying subvolumes and snapshots are important features of btrfs. Both operations are available to unprivileged users if the filesystem has been mounted with the "user_subvol_rm_allowed" mount option. Allow subvolume and snapshot deletion on idmapped mounts. This is a fairly straightforward operation since all the permission checking helpers are already capable of handling idmapped mounts. So we just need to pass down the mount's userns. In addition to regular subvolume or snapshot deletion by specifying the name of the subvolume or snapshot the BTRFS_IOC_SNAP_DESTROY_V2 ioctl allows the deletion of subvolumes and snapshots via subvolume and snapshot ids when the BTRFS_SUBVOL_SPEC_BY_ID flag is raised. This feature is blocked on idmapped mounts as this allows filesystem wide subvolume deletions and thus can escape the scope of what's exposed under the mount identified by the fd passed with the ioctl. Here is an example where a btrfs subvolume is deleted through a subvolume mount that does not expose the subvolume to be delete but it can still be deleted by using the subvolume id: /* Compile the following program as "delete_by_spec". */ #define _GNU_SOURCE #include #include #include #include #include #include #include #include #include static int rm_subvolume_by_id(int fd, uint64_t subvolid) { struct btrfs_ioctl_vol_args_v2 args = {}; int ret; args.flags = BTRFS_SUBVOL_SPEC_BY_ID; args.subvolid = subvolid; ret = ioctl(fd, BTRFS_IOC_SNAP_DESTROY_V2, &args); if (ret < 0) return -1; return 0; } int main(int argc, char *argv[]) { int subvolid = 0; if (argc < 3) exit(1); fprintf(stderr, "Opening %s\n", argv[1]); int fd = open(argv[1], O_CLOEXEC | O_DIRECTORY); if (fd < 0) exit(2); subvolid = atoi(argv[2]); fprintf(stderr, "Deleting subvolume with subvolid %d\n", subvolid); int ret = rm_subvolume_by_id(fd, subvolid); if (ret < 0) exit(3); exit(0); } #include " #include " #include sudo umount /mnt sudo mount ${LOOPDEV} -o subvol=B/C,user_subvol_rm_allowed /mnt ./delete_by_spec /mnt ${SUBVOLID} With idmapped mounts this can potentially be used by users to delete subvolumes/snapshots they would otherwise not have access to as the idmapping would be applied to an inode that is not exposed in the mount of the subvolume. The fact that this is a filesystem wide operation suggests it might be a good idea to expose this under a separate ioctl that clearly indicates this. In essence, the file descriptor passed with the ioctl is merely used to identify the filesystem on which to operate when BTRFS_SUBVOL_SPEC_BY_ID is used. Cc: Chris Mason Cc: Josef Bacik Cc: Christoph Hellwig Cc: David Sterba Cc: linux-btrfs@vger.kernel.org Signed-off-by: Christian Brauner --- fs/btrfs/ioctl.c | 26 ++++++++++++++++++++------ 1 file changed, 20 insertions(+), 6 deletions(-) diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c index 31115083f382..dd0fabdbeeeb 100644 --- a/fs/btrfs/ioctl.c +++ b/fs/btrfs/ioctl.c @@ -830,7 +830,8 @@ static int create_snapshot(struct btrfs_root *root, struct inode *dir, * nfs_async_unlink(). */ -static int btrfs_may_delete(struct inode *dir, struct dentry *victim, int isdir) +static int btrfs_may_delete(struct user_namespace *mnt_userns, + struct inode *dir, struct dentry *victim, int isdir) { int error; @@ -840,12 +841,12 @@ static int btrfs_may_delete(struct inode *dir, struct dentry *victim, int isdir) BUG_ON(d_inode(victim->d_parent) != dir); audit_inode_child(dir, victim, AUDIT_TYPE_CHILD_DELETE); - error = inode_permission(&init_user_ns, dir, MAY_WRITE | MAY_EXEC); + error = inode_permission(mnt_userns, dir, MAY_WRITE | MAY_EXEC); if (error) return error; if (IS_APPEND(dir)) return -EPERM; - if (check_sticky(&init_user_ns, dir, d_inode(victim)) || + if (check_sticky(mnt_userns, dir, d_inode(victim)) || IS_APPEND(d_inode(victim)) || IS_IMMUTABLE(d_inode(victim)) || IS_SWAPFILE(d_inode(victim))) return -EPERM; @@ -2914,6 +2915,7 @@ static noinline int btrfs_ioctl_snap_destroy(struct file *file, struct btrfs_root *dest = NULL; struct btrfs_ioctl_vol_args *vol_args = NULL; struct btrfs_ioctl_vol_args_v2 *vol_args2 = NULL; + struct user_namespace *mnt_userns = file_mnt_user_ns(file); char *subvol_name, *subvol_name_ptr = NULL; int subvol_namelen; int err = 0; @@ -2941,6 +2943,18 @@ static noinline int btrfs_ioctl_snap_destroy(struct file *file, if (err) goto out; } else { + /* + * Deleting by subvolume id can be used to delete + * subvolumes/snapshots anywhere in the filesystem. + * Ensure that users can't abuse idmapped mounts of + * btrfs subvolumes/snapshots to perform operations in + * the whole filesystem. + */ + if (mnt_userns != &init_user_ns) { + err = -EINVAL; + goto out; + } + if (vol_args2->subvolid < BTRFS_FIRST_FREE_OBJECTID) { err = -EINVAL; goto out; @@ -3025,7 +3039,7 @@ static noinline int btrfs_ioctl_snap_destroy(struct file *file, err = down_write_killable_nested(&dir->i_rwsem, I_MUTEX_PARENT); if (err == -EINTR) goto free_subvol_name; - dentry = lookup_one_len(&init_user_ns, subvol_name, parent, subvol_namelen); + dentry = lookup_one_len(mnt_userns, subvol_name, parent, subvol_namelen); if (IS_ERR(dentry)) { err = PTR_ERR(dentry); goto out_unlock_dir; @@ -3067,14 +3081,14 @@ static noinline int btrfs_ioctl_snap_destroy(struct file *file, if (root == dest) goto out_dput; - err = inode_permission(&init_user_ns, inode, + err = inode_permission(mnt_userns, inode, MAY_WRITE | MAY_EXEC); if (err) goto out_dput; } /* check if subvolume may be deleted by a user */ - err = btrfs_may_delete(dir, dentry, 1); + err = btrfs_may_delete(mnt_userns, dir, dentry, 1); if (err) goto out_dput;